• Thanks for visiting The Penturners Forum today.

    There are many features and resources that currently you are unable to see or access, either because you're not yet registered, or if you're already registered, because you're not logged in.

    To gain full access to the forum, please log in or register now. Registration is completely free, it only takes a few seconds, and you can join our well established community of like-minded pen makers.

Brass tubes and bushing fits

hawkeyefxr

hawkeyefxr

Full Member
Joined
Jan 8, 2015
Posts
373
Location
Yateley Hants
First Name
ken
I have noticed that some bushing kits fit better than others, what should be the clearance when the bushing is inserted into the brass tube.
Obviously if it's to loose you will have all sort of problems, if it's tight you will maybe expand the brass tube and wreck the pen before you get going.
 
silver

silver

General dogsbody
Executive Member
Joined
Jun 29, 2013
Posts
6,304
Location
Somewhere in Staffordshire,
First Name
Eamonn.
I don't believe there is a specific clearance that is specified Ken.

But in engineering terms a clearance fit, meaning it can be removed easily.

Some may correct me if I am wrong on this, but manufacturers tried the transition fit but that made the bushes tight and a little difficult to remove once finished on the lathe.

Basically the three fits are

Clearance, transition(or location fit) and interference.

I know it may not help but basically they should fit snugly inside the tubes with very little effort to fit and should have no play but be able to be removed easily.

If we get in to measuring them then you will have many a different result as it depends on what type of DIY tool you are using to measure them with. many manufacturers have tools that costs 1000 of £ to ensure that the tolerances are correct every single operation.

I'm sure someone will come on and tell you the specific clearance equation for each of the three states. For the hell of it I can't remember.
 
hawkeyefxr

hawkeyefxr

Full Member
Joined
Jan 8, 2015
Posts
373
Location
Yateley Hants
First Name
ken
silver said:
Here you got,

Just done a quick search.

Explains all the fits and the specified tolerance..

http://www.mmto.org/dclark/Reports/Encoder Upgrade/fittolerences [Read-Only].pdf
Click to expand...


I am/was an engineer myself, did the whole apprenticeship thing in the 60s. some of what i say will be in both languages, imperial and metric. (cant think in metric lol)

The brass tube will be extruded so will be pretty near the same size all the time.
In measuring the the bush spigot to the brass tube ID i get a difference of 0.4mm, thats about 18thou, a country mile in engineering when related to the size of tubing (8mm).
I have measured other brass tube and bushes and it come out at around 0.06mm, i call that ok.
With the making of pens i don't expect Swiss watch standards.

If i still had my Myford i would make my own.
 
silver

silver

General dogsbody
Executive Member
Joined
Jun 29, 2013
Posts
6,304
Location
Somewhere in Staffordshire,
First Name
Eamonn.
hawkeyefxr said:
I am/was an engineer myself, did the whole apprenticeship thing in the 60s. some of what i say will be in both languages, imperial and metric. (cant think in metric lol)

The brass tube will be extruded so will be pretty near the same size all the time.
In measuring the the bush spigot to the brass tube ID i get a difference of 0.4mm, thats about 18thou, a country mile in engineering when related to the size of tubing (8mm).
I have measured other brass tube and bushes and it come out at around 0.06mm, i call that ok.
With the making of pens i don't expect Swiss watch standards.

If i still had my Myford i would make my own.
Click to expand...
With your engineering head Ken 0.06 is as My link is probably nearest to the transition top end tolerances. So closer for an engineer to deal with.:tongue:

But yep, not Swiss watches but they should be closer than what you had on your measurement.

But then again it all depends on where you get the bushes and the kits from. I have had the same bushes from the same suppliers that have been different than the first ones they supplied. :rolling:

I have a Myford and used to make all our own bushes and fittings because they wasn't on the market like they are today.

I have tended to move towards supplied ones over the last 10years or so due to the many different kits out there now and I found I was spending more time making bushes than we were turning pens. Usually had to make two sets as well.:sob: for the price it wasn't too much to pay out.

The most important thing Ken is even with new kits on old bushes or new bushes on old kits, make sure you measure the kits against the bushes prior to turning them. If you don't you would have waisted so much time turning the pens only to find you have to re mount them and turn more off or realise that the barrels have been overturned and can't put it back on.:sob:
 
Penpal

Penpal

Grand Master
Joined
May 26, 2013
Posts
25,342
Location
Canberra AUSTRALIA
First Name
Peter
I made a simple holder for my pen tubes for roughing that tells me right then if the tube is correctly sized or not. I keep two or three hundred spare brasses of Slimline my most common pen. If it ,the brass is far too tight I pitch the brass in the bin.

The fit I crave is a smooth slip fit (my definition), ie holds on the holder.

In penmaking consistent sizing is a myth. Tolerances are there and about compared with metal work generally.

If you caliper your new drills be surprised even with the most expensive, the variations in true stated size matters.

So bushes may be accurate and brasses vary or vice versa, before and to be sure measure them it helps me.

Peter.
 
Warning! This thread has not had any replies for over a year. You are welcome to post a reply here, but it might be better to start a new thread (and maybe include a link to this one if you need to).
Top